Wickedly (10)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">wickedly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for badly that I've seen before include "Seriously; poorly" , "Severely; very much" , "Severely; seriously" .)
(Another definition for fiendishly that I've seen is " Infernally clever".)